An investigation of microscale explosive vaporization of water on an ultrathin Pt wire

The explosive vaporization of water close to its superheat limit was investigated at the microscale level using a short (I mm in length) and ultrathin (10 mum in diameter) Pt wire. It was possible to obtain novel visualizations and simultaneously pressure and temperature measurements in the vapor microregion, thus accomplishing a step forward in understanding the complex behavior of explosive vapor nucleation, growth, and subsequent collapse, despite experimental difficulties posed by the very short time and length scales of the phenomena. The temperature results verify (to the best of our knowledge, for the first time) the limit of superheat reported in the classical work of Skripov. The nucleation temperature increases with heating rate until a maximum limit is reached. The maximum heating rate was 86 x 10(6) K/s and a maximum nucleation temperature of 303 degreesC could be obtained. For the visualization of the very rapid boiling process, a strobe microscopy technique was developed and employed. A clear difference in the mode (homogeneous vs. heterogeneous) of vapor nucleation between high and moderate heating rates was observed. A fast pressure transducer allowed to capture the acoustic emission from the expanding vapor volume. From these data, the pressure inside the growing vapor layer and the mechanical energy released by its rapid expansion could be estimated. (C) 2001 Published by Elsevier Science Ltd.